Coupling with tribological coating system

ABSTRACT

A coupling with a tribological system that can withstand temperatures up to 600° C. The coupling includes a shaft having an outer surface with a layer of chromium and a sleeve for receiving the shaft. The sleeve has an inner surface with a layer of silver or gold. The silver or gold layer contacts the chromium layer to form the tribological system.

RELATED APPLICATIONS

[0001] This is a divisional of and claims priority from application Ser.No. 09/660,647 entitled “Coupling With Tribological Coating System”,filed Sep. 13, 2000, which is incorporated herein by reference.

TECHNICAL FIELD

[0002] This invention relates to couplings for rotating components suchas an electric generator shaft and a gearbox and in particular to atribological coating system for use on such couplings.

BACKGROUND OF THE INVENTION

[0003]FIGS. 1A and 1B show typical components of a coupling assembly forcoupling an electric generator shaft to a gearbox. The assembly includesa sleeve 10 having an axially extending portion 12 and a flange portion14. The axially extending portion 14 has a generally squarecross-section with the four corners beveled. The axially extendingportion 14 is inserted into a hollow section of an electric generatorshaft having the same cross-sectional shape. Also part of the assemblyis a drive shaft 20. The drive shaft 20 has a splined portion 22 forengaging corresponding splines in a gearbox. It also has an axiallyextending shaft portion 24 shaped and sized to be inserted into thesleeve 10.

[0004] During prolonged usage at high speeds and temperatures, thisprior art coupling assembly will experience wear on the contactingsurfaces. This wearing may result in the binding of the shaft portion 24and/or the tearing of the sleeve 10.

[0005] Accordingly, there exists a need for a coupling assembly having atribological system that can operate at high temperatures and speed.

SUMMARY OF THE INVENTION

[0006] An object of the present invention is to provide a couplingassembly having a tribological system that can operate at hightemperatures and speed.

[0007] The present invention achieves this object by providing acoupling with a tribological system that can withstand temperatures upto 600° C. The coupling includes a shaft having an outer surface with alayer of chromium and a sleeve for receiving the shaft. The sleeve hasan inner surface coated with a layer of silver or gold. The silver orgold layer contacts the chromium layer to form the tribological system.

[0008] These and other objects, features and advantages of the presentinvention are specifically set forth in or will become apparent from thefollowing detailed description of a preferred embodiment of theinvention when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1A is a perspective view of a prior art sleeve.

[0010]FIG. 1B is a perspective view of a prior art drive shaft.

[0011]FIG. 2 is an exploded, cross-sectional view of the couplingassembly contemplated by the present invention.

[0012]FIG. 3 is a plot of test data from the testing of a couplingassembly contemplated by the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013] Referring to FIG. 2 a coupling assembly for coupling a electricgenerator shaft 30 to a gearbox 32 is generally denoted by referencenumeral 40. The assembly 40 includes a sleeve 42 having an axiallyextending portion 44 and a flange portion 46. The axially extendingportion 44 has a generally square cross-section with the four cornersbeveled. The sleeve 42 is preferably formed of aluminum bronze.Alternatively, the sleeve 42 can be formed of brass (Cu-Zn) alloys, tinbronze (Cu-Sn) alloys or other copper beryllium alloys. The axiallyextending portion 44 is inserted into a hollow section 31 of theelectric generator shaft 30. The hollow section 31 having the samecross-sectional shape as the shaft portion 44. The assembly alsoincludes a drive shaft 50. The drive shaft 50 has a splined portion 52for engaging corresponding splines in the gearbox 32. It also has anaxially extending shaft portion 54 shaped and sized to be inserted intothe axially extending portion 44 of the sleeve 42. The drive shaft 50 ispreferably formed of a steel alloy.

[0014] Disposed between the axially extending portion 44 and the axiallyextending shaft portion 54 is a tribological system that can withstandprolonged high speed and high temperature operation. The tribologicalsystem is comprised of a chromium layer 60 on the outer surface of theaxially extending shaft portion 54 and a silver layer 62 on the innersurface of the axially extending shaft portion 44. Alternatively, thelayer 62 can be gold. The layer gold or silver is preferably puremeaning that impurities are at most 1% of the composition. The silver,gold and chromium are preferably applied to their respective surfaces byplating processes familiar to those skilled in the art. The silver orgold plating is metallurgically bonded to the shaft portion 44 by heattreating at 600° C. for ½ hour. Alternatively, the layers may be appliedby other techniques such as evaporation or physical vapor deposition. Inthe preferred embodiment, the thickness of the chromium layer 60 is inthe range of 0.0005 to 0.002 inch with 0.001 inch being the preferred.Likewise, the thickness of the silver or gold layer 62 is in the rangeof 0.0005 to 0.002 inch with 0.001 inch being the preferred.

[0015]FIG. 4 is a plot of test data taken from the testing of thecoupling assembly contemplated by the present invention. The X-axisshows temperature and the Y-axis coefficient of friction. The data showsthat within experimental error the coefficient stayed unchanged even attemperatures up to 600° C.

[0016] Thus a coupling assembly is provided that can operate attemperatures as high as 600° C. without galling, loss of surface finishor significant wearing of either the sleeve or the drive shaft.

[0017] Though the invention has been described with respect to thesquare shaped components used in coupling a generator to a gearbox, itshould be appreciated that the invention is applicable to the couplingof other components independent of cross-sectional shape. Thus, thisdescription of the preferred embodiment should be considered exemplaryand not as limiting the scope and spirit of the invention as set forthin the following claims.

What is claimed is:
 1. A coupling assembly comprising: a shaft having anouter surface with a layer of chromium; and a sleeve for receiving saidshaft and having an inner surface with a layer of gold, said gold layercontacting said chromium layer to form a tribological system.
 2. Thecoupling assembly of claim 1 wherein said sleeve is of a materialselected from a group consisting of aluminum bronze, brass, tin bronzeand copper beryllium.
 3. The coupling assembly of claim 2 wherein saidshaft is made of a steel alloy.
 4. The coupling assembly of claim 1wherein said sleeve is of aluminum bronze.
 5. The coupling assembly ofclaim 1 wherein the thickness of the chromium layer is in the range of0.0005 to 0.002 inch.
 6. The coupling assembly of claim 1 wherein thethickness of the silver layer is in the range of 0.0005 to 0.002 inch.